1. Field of the Invention
The present invention relates to a method for phaseaccurate imaging and measuring of elastic wave fields with a laser probe in which elastic waves are excited on a specimen, in which a laser beam is directed onto the specimen surface, in which the deflection of the reflected laser beam caused by an undulation of the specimen surface is detected, and in which a measured signal proportional to the undulation is generated. Apparatus for implementing the method is provided along with an optical system for focusing the laser beam onto the specimen surface. A radiation detector documents the deflection of the reflected laser beam produced by the undulation of the specimen surface, and a device generates a measured signal proportional to the undulation.
2. Description of the Prior Art
Components in which elastic waves, particularly acoustic surface waves, are excited by transducer structures on piezoelectric materials and are detected are acquiring increasing significance in communications and high-frequency technology. Since planar technology allows an extremely accurate and economical manufacture of these systems, the same have been optimized with the assistance of the methods of computer-aided design (CAD). Since the models employed for the calculation of the wave propagation do not consider all physical effects (reflections at edges, diffraction phenomena, etc), deviations between realized and desired component behavior frequently occur. For improving the CAD models, it is therefore necessary to image the wave field in the component with accurate phase or, respectively, to measure the parameters that characterize the elastic wave (amplitude, phase, propagation speed) topically resolved.
IEEE Transactions on Sonics and Ultrasonics, Vol. SU-25, No. 6, 1978, pp. 372-377, describes a method for imaging acoustic surface wave fields in which the Surface Acoustic Wave (SAW) component is scanned point-by-point with an intensity-modulated laser beam. The imaging of a large wave field is extremely time consuming since the acquisition of the measured value requires a few seconds at each of the respective scan locations.